CN112378956A - Low-temperature gas humidity measuring system and method - Google Patents
Low-temperature gas humidity measuring system and method Download PDFInfo
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- CN112378956A CN112378956A CN202011187896.0A CN202011187896A CN112378956A CN 112378956 A CN112378956 A CN 112378956A CN 202011187896 A CN202011187896 A CN 202011187896A CN 112378956 A CN112378956 A CN 112378956A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N25/00—Investigating or analyzing materials by the use of thermal means
- G01N25/56—Investigating or analyzing materials by the use of thermal means by investigating moisture content
- G01N25/66—Investigating or analyzing materials by the use of thermal means by investigating moisture content by investigating dew-point
- G01N25/68—Investigating or analyzing materials by the use of thermal means by investigating moisture content by investigating dew-point by varying the temperature of a condensing surface
Abstract
The invention provides a system and a method for measuring humidity of low-temperature gas, comprising the following steps: the principle of a cold mirror dew point method is utilized to convert the measurement of gas humidity into the measurement of dew point temperature; the dew point generating device comprises a low-temperature control platform and a cold mirror, the low-temperature control platform is placed on an objective table of the low-temperature control platform, the dew point generating and detecting system comprises a laser transmitter and a photoelectric detector, the laser transmitter and the photoelectric detector are externally connected outside a vacuum cover of the low-temperature control platform through optical through holes, light emitted by the laser transmitter enters the cold mirror through the optical through holes, enters the photoelectric detector with an optical filter after being reflected, and the dew point is judged to be generated through obvious signal change of the photoelectric detector. According to the invention, when the low-temperature control platform is cooled to the extremely low temperature, the laser emitter and the photoelectric detector still work at the normal temperature, and the dew point forming temperature on the cold mirror is accurately measured, so that more accurate gas humidity can be deduced.
Description
Technical Field
The invention relates to the field of low-temperature measurement, in particular to a system and a method for measuring gas humidity at low temperature by using a cold mirror dew point method.
Background
With the continuous development of technologies such as superconduction and nuclear fusion in the low-temperature field, the requirements on the precision and stability of temperature control are gradually improved, and the performance requirements of a deep low-temperature sensor in a deep low-temperature region (a temperature region close to absolute zero degree) are correspondingly improved. In the calibration of the deep low temperature sensor, the measured temperature sensor is usually placed on an objective table in a vacuum cavity, the objective table is connected with a refrigerator, the temperature on the objective table is reduced by refrigeration and conduction through a compressor, and the temperature sensor and a heater near the objective table are used for controlling the temperature, so that the calibration of different temperature points of the temperature sensor is realized. The temperature characteristic curve of the temperature sensor and the temperature cycle impact of the temperature sensor are generally measured by using a low-temperature control platform. During measurement in a low-temperature area, even if the air pressure in the cavity is pumped to be extremely low (100Pa), the temperature control of the platform is still unstable occasionally, oxygen condensation is one of the reasons for temperature drift or unstable temperature reduction, and a method is needed for measuring the oxygen humidity in the cavity so as to eliminate or avoid the influence of the oxygen humidity.
The cold mirror dew point method is a mature method for measuring humidity, and in the national standard GB/T27895-2011 and the national measurement standard JJJG 499-2004 'visual measurement method for measuring the dew point of the natural gas hydrocarbon cooling mirror surface' and 'verification procedure for a precise dew point instrument', the description that the measured humidity of a certain gas is the ratio of the gas vapor pressure at the current temperature to the saturated vapor pressure at the current temperature is calculated; the cold mirror dew point method is to cool the mirror surface, when the gas dews on the surface of the mirror surface, the gas reaches saturated vapor pressure at the temperature, the temperature is the dew point temperature, the saturated vapor pressure A corresponding to the temperature is obtained through a formula after the temperature is measured, the content of the corresponding gas is obtained, and the ratio of the A to the saturated vapor pressure of the gas at normal temperature is calculated to obtain the humidity of the gas at normal temperature. Both standards are based on measurements taken at around atmospheric pressure to ensure that the gas flows so that the pressure remains constant over a period of time. The two methods can respectively observe whether the dew point is formed by visual inspection or a method of establishing a laser sensor-reflector-photoelectric detector optical path in the dew point instrument and observing the output parameters of the photoelectric detector. The dew point measurement ranges of the two methods are about-40 ℃ to +40 ℃, heat transfer can be caused due to the increase of gas density, and the temperature can not be reduced to lower temperature, and if the gas pressure is reduced, the dew point temperature can also be correspondingly reduced, and the temperature can not be reduced due to the limitation of instruments.
The search of the prior art shows that the data provided by the 'comparison of national values and result analysis' of the precision dew point instrument 'written by Zhang Wendong et al in Industrial metrology' indicates that the measured dew point range of the domestic precision dew point instrument is generally not more than-20-40 ℃. The inventor's book of "automatic detection method for measuring dew point of natural gas hydrocarbon" on cooling mirror surface surpassed in "industrial metrology", which proves that the dew point method is also suitable for measuring the humidity of other gases (such as natural gas hydrocarbon) except water vapor, and the dew point measurement range is about-40 to 4 ℃. In summary, the currently reported cold mirror dew point method cannot measure the oxygen content under the near vacuum condition because the corresponding dew point temperature may be near-253.16 ℃, and the common temperature measuring and controlling device cannot reach the temperature and ensure the temperature controlling precision.
Disclosure of Invention
Aiming at the defects in the field of low-temperature measurement in the prior art, the low-temperature control platform can provide temperature precision control of the low-temperature region, the low-temperature control platform is combined with a cold mirror dew point method, and meanwhile, the problem that a common laser transmitter and a photoelectric detector cannot exert the performance of the common laser transmitter and the photoelectric detector at low temperature is considered, so that a normal-temperature running environment is created.
The humidity referred to in daily life is a relative humidity and is generally expressed as RH, and is a percentage of the amount of water vapor (water vapor pressure) contained in the air to the saturated amount of water vapor (saturated water vapor pressure) in the same case. The "gas humidity" in the present invention refers to the percentage of the gas in the chamber to the vapor pressure of the gas saturated in the chamber, and is also expressed by RH. The dew point temperature is the temperature at which the water vapor is cooled to saturation and is converted into equilibrium with the physical state of water. The dew point temperature refers to the temperature at which the gas in the cavity is cooled to a saturated state and is converted into a liquid form of the gas to reach an equilibrium state.
In a first aspect, the present invention provides a cryogenic gas humidity measurement system comprising:
the dew point generating device is used for generating a dew point and comprises a low-temperature control platform and a cold mirror with a polishing surface, the low-temperature control platform is provided with a closed cavity, and the closed cavity is provided with a refrigerating device used for reducing the temperature of the cold mirror and a temperature control assembly used for controlling the cooling speed; the low-temperature control platform is externally connected with a measuring component for measuring air pressure and a vacuum pump for adjusting the air pressure of the closed chamber; the cold mirror is arranged in the closed cavity as a reflecting mirror surface, and a first temperature sensor is arranged on the cold mirror and used for collecting the surface temperature value of the cold mirror;
a dew point detecting system for judging whether generate dew point, dew point detecting system includes laser emitter and the photoelectric detector who assembles the light filter, laser emitter photoelectric detector symmetry set up in the airtight cavity outside of low temperature accuse temperature platform, by laser emitter cold mirror reaches photoelectric detector forms the light path, wherein laser emitter launches laser warp low temperature accuse temperature platform extremely cold mirror, warp cold mirror reflection extremely photoelectric detector, through photoelectric detector signal obviously changes and judges dew point and generates, according to surveying dew point formation temperature on the cold mirror to obtain the gas humidity that awaits measuring.
The laser emitter and the photoelectric detector are symmetrically arranged outside the closed cavity of the low-temperature control platform, and the temperature of the formed dew point and the temperature of the vanished dew point can be measured most accurately.
Preferably, the low temperature control platform comprises:
the vacuum cover is provided with an accommodating cavity, and a first optical through hole for passing through the light path is formed in the top of the vacuum cover; the vacuum cover is provided with a first vacuum port and a second vacuum port which are respectively externally connected with a vacuum gauge and a tee joint;
the objective table is arranged in the accommodating cavity of the vacuum cover, is a cold transfer and temperature fluctuation inhibition assembly and is used for bearing the cold mirror;
the low-temperature radiation cold screen is arranged in the accommodating cavity of the vacuum cover, the low-temperature radiation cold screen covers the outer portion of the objective table and forms a closed space with the objective table, a second optical through hole used for passing through the light path is formed in the top of the low-temperature radiation cold screen, and the position of the second optical through hole is opposite to that of the first optical through hole from top to bottom. All set up central optics through-hole at vacuum cover top and low temperature radiation cold shield for the light path can normally pass through, also makes laser emitter and photoelectric detector external cover in the vacuum outside, makes photoelectric detector and laser emitter itself needn't need low temperature resistant characteristic, reduces the experiment cost, does benefit to the adjustment light path angle at any time simultaneously.
Preferably, the laser emitter and the photodetector are disposed outside the vacuum hood and located on two sides of the first optical through hole, and the light path is formed by the laser emitter, the first optical through hole, the second optical through hole, the cold mirror, the second optical through hole, the first optical through hole and the photodetector in sequence.
Preferably, a first channel of a tee joint externally connected with the second vacuum port is sequentially connected with the first stop valve and the vacuum pump through pipelines, and a second channel of the tee joint is sequentially connected with the micro-regulating valve, the second stop valve, the pressure reducing valve and the gas storage device through pipelines.
Preferably, the temperature control assembly is embedded in the objective table, the control assembly comprises a heater and a second temperature sensor, the second temperature sensor is arranged above the heater, and the second temperature sensor is positioned right below the cold mirror;
more preferably, the heater and the second temperature sensor are disposed at the midpoint of the stage, and are embedded in the stage from above and below, respectively, so that temperature control is more uniform.
Preferably, the refrigeration device is disposed below the stage.
Preferably, by adjusting the incident angle of the optical path, the reflected light is perpendicular to the receiving plane of the photodetector, so that the interference of the light reflecting surface and other light sources to the photodetector can be reduced;
the wavelength of the laser emitter is matched with the wavelength range of the optical filter of the photoelectric detector, so that the photosensitive object of the photoelectric sensor is ensured to be incident light of the laser emitter. More preferably, the laser emitter can adopt a dot laser emitter with the diameter smaller than 1mm, the wavelength of the laser emitter is matched with that of the filter plate, and the light spot is matched with the size of the collection opening of the photoelectric detector, so that the light path is clear and measurable.
The interference of the reflecting surface and other light sources to the photoelectric detector can be reduced by adjusting the incident angle of the light path and adopting the design of the optical filter.
Preferably, the photoelectric detector is externally connected with an oscilloscope or a voltage acquisition card for observing signal changes, and data in a period of time are acquired and recorded so as to calculate the time for dew elimination and dew condensation. When the dew point is measured, an oscilloscope is used for recording data of the photoelectric detector and drawing a curve, so that errors caused by naked eyes can be reduced, the time of dew condensation and dew elimination and the dew point temperature can be accurately observed, and the time and the dew point temperature are mutually verified with the naked eyes.
The second aspect of the invention is to provide a method for measuring the humidity of low-temperature gas, which is implemented by adopting the system for measuring the humidity of low-temperature gas, and converting the measurement of the humidity of gas into the measurement of dew point temperature by using a cold mirror dew point method; the gas to be detected is a gas with a normal pressure dew point of less than 25 ℃, and the gas comprises but is not limited to any one of oxygen, argon, nitrogen, carbon dioxide or helium.
Preferably, the low temperature gas humidity measuring method comprises the steps of:
s1: the polishing surface of the cold mirror faces upwards, and the other surface of the cold mirror is connected to an objective table of a low-temperature control platform by using low-temperature heat-conducting glue;
preferably, in S1, the cold mirror may use a single-sided polished mirror as the reflective mirror surface, but the method is not limited to use of a single-sided polished mirror surface, and may also be applied to a double-sided polished mirror surface; the mirror material is suitable for all materials which can be used as a reflector and have good heat-conducting property, such as red copper, aluminum, silicon wafers and the like.
S2: the method comprises the following steps that low-temperature sensors are symmetrically arranged on the edge of a cold mirror polishing surface, and the bottom surface of each low-temperature sensor is fixed with the cold mirror polishing surface through low-temperature heat conduction glue, so that the bottom surface of each low-temperature sensor is enabled to be tightly attached to the cold mirror polishing surface; the temperature of the formed dew point and the temperature of the vanished dew point can be measured most accurately by adopting the symmetrically arranged temperature sensors in the step.
S3: a first optical through hole and a second optical through hole are respectively arranged at the top of the vacuum cover and the top of the low-temperature radiation cold screen, and a laser emitter and a photoelectric detector are respectively and symmetrically arranged at two sides of the first optical through hole to form a light path of the laser emitter, the first optical through hole, the second optical through hole, a cold mirror reflection, the second optical through hole, the first optical through hole and the photoelectric detector;
preferably, in S3, the diameters of the first optical through hole and the second optical through hole are both 2cm to 10cm, where the second optical through hole of the low-temperature radiation cold shield may be implemented by using through holes; the first optical through hole of the vacuum cover can be realized by adopting materials with good light transmission such as plane glass, so that the light path can normally pass through the first optical through hole and is not limited to the diameter of the optical through hole.
In the above-mentioned S3, laser emitter and photoelectric detector are externally connected outside the vacuum cover, so that photoelectric detector and laser emitter do not need low temperature resistance, the experiment cost is reduced, and the light path angle can be adjusted at any time.
More preferably, in S3, the light path may be interfered by a plurality of reflective surfaces, and by adjusting the incident angle of the light path, the light path of "laser emitter-first optical via-polished copper mirror reflection-second optical via-photodetector" can be clearly seen, and the reflected light should be perpendicular to the receiving plane of the photodetector. At the moment, the light paths reflected by the upper surface and the lower surface of the plane glass cannot irradiate the photoelectric detector, and the result is influenced. The interference of the reflecting surface and other light sources to the photoelectric detector can be reduced by adjusting the incident angle of the light path and adopting the design of the optical filter.
More preferably, in S3, the wavelength of the laser emitter is matched with the wavelength range of the optical filter, so as to ensure that the object sensed by the photosensor is incident light of the laser emitter. The diameter and shape of the photosensitive opening are not limited to the light spot. A dot laser emitter with a diameter of less than 1mm may be used.
More preferably, in S3, the photodetector is externally connected to an oscilloscope, but is not limited to an external oscilloscope, and an instrument suitable for observing signal changes, such as a voltage acquisition card, may also be used. When the dew point is measured, an oscilloscope is adopted to record data of the photoelectric detector and draw a curve, so that errors caused by naked eyes can be reduced, the time of dew condensation and dew elimination and the dew point temperature can be accurately observed, and the time and the dew point temperature are mutually verified with the naked eyes.
S4: connecting a first vacuum port of the low-temperature control platform with a vacuum gauge and connecting a second vacuum port of the low-temperature control platform with a tee joint, wherein a first channel of the tee joint is sequentially connected with a first stop valve and a vacuum pump, and a second channel is sequentially connected with a micro-regulating valve, a second stop valve, a pressure reducing valve and a gas storage device; then introducing gas to be detected into the vacuum cover for 3-5 minutes through a second channel, and then closing the micro-regulating valve, the second stop valve and the pressure reducing valve in sequence;
more preferably, the S4 is a tee joint, so that the two functions of vacuum pumping and gas introduction are the same pumping port and do not interfere with each other. The method comprises the combination of the two functions, including the method of only vacuumizing or only passing the gas to be measured.
The S4 can ensure that the gas to be detected has high purity and no impurities in the gas pipe, and can micro-control the content of the input gas, so that the method can measure the humidity of the gas to be detected with different concentrations. When the vacuum pumping and the gas introduction are switched, because the vacuum gauge is used and is not provided with a three-way vacuum pumping port, the air pressure in the low-temperature control platform can be measured normally, and the phenomenon that the concentration of the gas to be measured is excessive and loses the heat insulation effect is avoided.
S5: opening a vacuum pump, vacuumizing, closing the vacuum pump, opening a refrigerating device of a low-temperature control platform to cool the low-temperature control platform, starting a temperature control assembly after the low-temperature control platform is cooled to a set temperature, controlling the cooling speed of the low-temperature control platform to enable the low-temperature control platform to cool at a constant speed until a dew point appears, enabling the indication number of a photoelectric detector to change, enabling the polished surface of the cold mirror to be observed to be fogged by naked eyes, and recording the temperature value of a first temperature sensor at the moment as the current dew point temperature; continuing to cool the low-temperature control platform to a set temperature, then carrying out uniform temperature rise operation until the dew point disappears, and recording the temperature value of the first temperature sensor at the moment;
s6: continuing to heat the low-temperature control platform to a set temperature, repeating the operations of cooling and heating and recording the temperature value with the dew point and the temperature value with the dew point disappearing, and taking the average value of a plurality of recorded temperature values as the dew point temperature value at the moment as the time delay condition of human eye error or photoelectric detector capture caused by the dew point disappearing or appearing phenomenon is recorded during the heating and cooling;
more preferably, the air pressure required for the temperature reduction in S6 is determined in practice as long as the temperature can be reduced below the dew point temperature; the temperature capable of reducing speed is also based on the actual situation, the air pressure is displayed by a vacuum gauge as the current gas vapor pressure, the temperature reaching the saturated gas vapor pressure (dew point) to be measured is estimated by a formula, and the speed is reduced near a certain temperature higher than the temperature point.
S7: according to the calculation relationship between the dew point temperature and the saturated vapor pressure of the gas to be measured, the saturated vapor pressure of the gas to be measured in the cavity is converted, namely the content of the gas in the cavity, and meanwhile, the humidity of the gas at any temperature can be obtained.
Preferably, the low temperature gas humidity measuring method includes:
when the relation between the humidity and the dew point temperature of the gas to be detected with different concentrations needs to be researched, under the condition that a first stop valve connected with a vacuum pump is closed in S4, a second stop valve and a pressure reducing valve of a gas storage device are unscrewed for a set angle, the gas to be detected is introduced at the minimum flow of an adjusting valve, and the situation that the vacuum degree is insufficient due to the fact that the concentration of the gas to be detected is too high is prevented; and repeating the steps S5, S6 and S7 to measure the dew point temperature corresponding to the gas concentration, thereby measuring the humidity of the gas to be measured with different concentrations. In the step, the content of the input gas is controlled in a micro-scale manner, so that the method can measure the humidity of the gas to be measured with different concentrations, and the phenomenon that the heat insulation effect is lost due to the excessive concentration of the introduced gas is avoided.
According to the method for measuring the humidity of the low-temperature gas, the concentration of the current gas to be measured is determined by adopting the relation between the saturated vapor pressure concentration of the gas to be measured and the temperature, namely the condensation phenomenon is generated when the current gas to be measured reaches the saturated vapor pressure due to the fact that the temperature is reduced, and the measured temperature can be used for reversely calculating the saturated vapor pressure of the current gas to be measured, namely the vapor pressure of the gas to be measured at the normal temperature.
Compared with the prior art, the invention has at least one of the following beneficial effects:
according to the measuring system, the principle of a cold mirror dew point method is utilized, gas humidity measurement is converted into dew point temperature measurement, and the dew point temperature measurement is realized by arranging a dew point generating device and a dew point detecting system; by arranging the refrigerating device and the temperature control assembly, the cooling or heating speed can be adjusted, repeated measurement can be carried out near a temperature node where dew point is generated and disappears, and the measurement precision is improved; the laser emitter and the photoelectric detector are arranged externally, so that the laser emitter and the photoelectric detector work at a normal temperature state, the low-temperature control platform is cooled to an extremely low temperature, the dew point forming temperature on the cold mirror is accurately measured at the moment, and the accurate humidity of the gas to be measured can be deduced; and no additional wiring is required for the laser emitter and photodetector.
According to the measuring system, the low-temperature control platform is externally connected with the gas storage device, the gas concentration can be subjected to micro-adjustment by arranging the micro-adjustment valve, and the relationship between different gas concentrations and dew point temperatures is explored by measuring the humidity of different gas concentrations; and the problem that the heat conduction cannot keep low temperature when the concentration of the introduced gas is too high and exceeds a certain limit is solved, and the phenomenon that the concentration of the introduced gas loses the heat insulation effect is avoided.
Drawings
Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:
FIG. 1 is a front cross-sectional view of a cryogenic gas humidity measurement system according to a preferred embodiment of the present invention;
FIG. 2 is a schematic diagram of the vacuum pump connection of the cryogenic gas humidity measurement system according to a preferred embodiment of the present invention;
FIG. 3 is a schematic view of the gas inlet piping connections of the cryogenic gas humidity measurement system according to a preferred embodiment of the present invention;
the scores in the figure are indicated as: the device comprises a laser emitter 1, a photoelectric detector 2, a light filter 3, a vacuum cover 4, a low-temperature radiation cold screen 5, an objective table 6, a tee joint 7, a refrigerating device 8, a first vacuum port 9, a temperature control assembly 10, a first temperature sensor 11, a cold mirror 12, a second optical through hole 13 and a laser light path 14, wherein the laser emitter is arranged on the laser light path; 15 is a first optical through hole, 16 is a first stop valve, 17 is a vacuum bellows, 18 is a vacuum pump, 19 is a connection port of a second channel, 20 is a KF25 flange, 21 is a micro-regulating valve, 22 is a second stop valve, and 23 is a pressure reducing valve; 24 is a gas storage device, 25 is a gas pipe, and 26 is a quick-screwing interface.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that variations and modifications can be made by persons skilled in the art without departing from the spirit of the invention. All falling within the scope of the present invention.
Referring to fig. 1, a schematic structural diagram of a low-temperature gas humidity measuring system according to a preferred embodiment of the present invention is shown, which includes a dew point generating device composed of a low-temperature control platform and a cold mirror 12 with a polished surface, for generating a dew point; and the dew point detection system consists of a laser transmitter 1 and a photoelectric detector 2 and is used for judging whether a dew point is generated or not.
Wherein, the low temperature accuse temperature platform is equipped with airtight cavity, and airtight cavity is equipped with the refrigerating plant 8 that is used for reducing cold mirror 12 temperature and is used for controlling the accuse temperature subassembly 10 of cooling speed. The low temperature control platform is externally connected with a measuring component for measuring the air pressure of the closed chamber, and the measuring component can adopt a vacuum gauge. The low temperature control platform is also externally connected with a vacuum pump 18 for adjusting the air pressure of the closed chamber.
The cold mirror 12 is arranged in the closed cavity, the cold mirror 12 is provided with a first temperature sensor 11, and the first temperature sensor 11 is used for collecting the surface temperature value of the cold mirror 12. The cold mirror 12 can be fixed on the objective table 6 of the low-temperature control platform by adopting low-temperature heat-conducting glue. The objective table 6 is cooled by the refrigerating device 8, the cold mirror 12 is cooled by conduction of the objective table 6, and when the temperature is reduced to a certain temperature, the gas reaches saturated vapor pressure at the temperature when the gas is condensed on the surface of the cold mirror 12, namely, dew point is generated. As a preferred mode, the cold mirror 12 may be a single-side polished copper mirror. The first temperature sensor 11 may be a zirconium oxynitride low-temperature sensor of SD Package (spring Dual-In-Line Package). During specific implementation, the SD-packaged zirconium oxynitride low-temperature sensor is symmetrically arranged at the edge of the polished surface of the copper mirror and is fixed by low-temperature heat-conducting glue, so that the bottom surface of the zirconium oxynitride low-temperature sensor is ensured to be tightly attached to the polished surface of the copper mirror.
The laser emitter 1 and the photoelectric detector 2 are symmetrically arranged outside a closed chamber of the low-temperature control platform, the photoelectric detector 2 is provided with the optical filter 3 with the central wavelength consistent with that of the laser emitter 1, and the laser emitter 1, the cold mirror 12 and the photoelectric detector 2 form a laser light path 14. Laser emitted by the laser emitter 1 passes through the low-temperature control platform to the cold mirror 12, is reflected and enters the photoelectric detector 2 provided with the optical filter 3, and whether a dew point is generated can be judged through obvious signal change of the photoelectric detector 2. This mode makes laser emitter 1 and photoelectric detector 2 work when normal atmospheric temperature state, and under the low temperature accuse temperature platform cooled down extremely low temperature, accurate dew point formation temperature on surveying cold mirror 12 this moment to can deduce the gas humidity that awaits measuring comparatively accurately. In a specific embodiment, the laser emitter 1 and the photodetector 2 may adopt the following parameters: the wavelength of the laser emitter 1 is 635nm, the light spot is a circular point, and the diameter is within 1 mm. The diameter of a light sensing opening of the photoelectric detector 2 is 3mm-5mm, the external central wavelength is 636nm, the half-width interval is 10nm of the optical filter 3, and the light sensing object of the sensor is ensured to be incident light of the laser emitter 1. However, the above system is not limited to the laser emitter 1 with wavelength of 635nm, and can be applied to all wavelength laser emitters 1, and matched filters and photodetectors 2, and is not limited to light spots, and the diameter and shape of the photosensitive opening.
The gas to be measured in the above embodiment may be oxygen, argon, nitrogen, carbon dioxide, helium, or other gas having a normal pressure dew point of less than 25 ℃.
In other partially preferred embodiments, the cold mirror 12 may use a double-sided cold mirror 12 side in addition to a single-sided polished copper mirror as the mirror surface; the method is not limited to the use of copper mirrors as the reflector surfaces, but is also applicable to all materials which can be used as the reflector surfaces and have good heat-conducting property, such as red copper, aluminum, silicon wafers and the like.
In some other preferred embodiments, the cryogenic temperature controlled platform comprises: a vacuum cover 4, a low-temperature radiation cold screen 5 and an objective table 6; wherein, the vacuum cover 4 is provided with a closed accommodating cavity. Preferably, the vacuum housing 4 has a rectangular parallelepiped structure. A first optical through hole 15 is provided at the top of the vacuum enclosure 4. An optical through hole is formed in the center of the top of the vacuum cover 4 by using a material with good light transmittance such as plane glass. The diameter of the first optical through hole 15 is 2cm to 10cm so that the optical path can normally pass through.
The objective table 6 is arranged in the accommodating cavity, the objective table 6 is a cold transmission and temperature fluctuation inhibition assembly, and the objective table 6 is used for bearing the cold mirror 12. The cold mirror 12 is fixed on the objective table 6, and the objective table 6 is cooled and conducted to the cold mirror 12 through the objective table 6, so that the cold mirror 12 is cooled.
The low-temperature radiation cold screen 5 is arranged in the accommodating cavity, the low-temperature radiation cold screen 5 has low-temperature radiation energy, and the low-temperature radiation cold screen 5 is covered outside the objective table 6 to form a closed space. The top of the low-temperature radiation cold screen 5 is provided with a second optical through hole 13, and the position of the second optical through hole 13 is opposite to the position of the first optical through hole 15. A second optical through hole 13 is formed by opening a through hole at the center of the top of the low-temperature radiation cold shield 5, and incident light or reflected light can pass through the second optical through hole 13 to the cold mirror 12 or to the photodetector 2. The diameter of the second optical through hole 13 is 2-10 cm.
In other preferred embodiments, the laser emitter 1 and the photodetector 2 are disposed on the top of the vacuum enclosure 4 and located on two sides of the first optical through hole 15, respectively, and the laser emitter 1, the first optical through hole 15, the second optical through hole 13, the cold mirror 12, the second optical through hole 13, the first optical through hole 15, and the photodetector 2 sequentially form a light path. In the specific implementation, the laser emitter 1 and the photodetector 2 can be mounted on the top of the vacuum enclosure 4 through a bracket, and the incident angle of incident light can be adjusted by adjusting the bracket. Connect laser emitter 1 and photoelectric detector 2 external in vacuum cover 4 outsidely for photoelectric detector 2 and laser emitter 1 itself needn't need low temperature resistant characteristic, reduce the experiment cost, do benefit to the light path angle of adjustment at any time simultaneously.
In other preferred embodiments, the light path may be interfered by a plurality of reflective surfaces, and the laser light path 14 of the laser emitter 1, the first optical through hole 15, the second optical through hole 13, the cold mirror 12, the second optical through hole 13, the first optical through hole 15 and the photodetector 2 "can be clearly seen by adjusting the incident angle of the light path. The reflected light should be perpendicular to the receiving plane of the photodetector 2. At this time, the light path reflected by the upper and lower surfaces of the plane glass of the first optical through hole 15 will not irradiate the photodetector 2, and the result will be affected.
In other partially preferred embodiments, referring to fig. 1, the vacuum cap 4 is provided with a first vacuum port 9 and a second vacuum port, wherein the first vacuum port 9 is used for connecting a vacuum gauge and the second vacuum port is used for connecting the tee joint 7. Referring to fig. 2, a first passage of the three-way valve 7 connects a first shut-off valve 16 and a vacuum pump 18 through a vacuum bellows 17, and the first shut-off valve 16 is disposed near the second vacuum port. Referring to fig. 3, the connection port 19 of the second channel of the three-way valve 7 is connected to the micro-adjustment valve 21, the second stop valve 22, the pressure reducing valve 23, and the gas storage device 24 in this order via the gas pipe 25. The micro-adjustment valve 21 may also be connected to the quick-turn port 26 via a KF25 flange 20. And a tee joint 7 is adopted, so that the two functions of the vacuumizing body and the ventilating body adopt the same vacuumizing opening and are not interfered with each other. In a specific measurement method, measurement can be performed by using all combination modes of the two functions, or measurement can be performed by only vacuumizing or only introducing gas, and the measurement method can be selected according to actual requirements. The micro-regulating valve 21 is arranged in the 25 way of the air inlet pipe of the second channel, so that the input gas content can be controlled in a micro mode, the gas content with different concentrations can be measured, and meanwhile, the phenomenon that the heat insulation effect is lost due to the fact that the gas concentration is excessive can be avoided.
In some other preferred embodiments, the temperature control assembly 10 is embedded in the stage 6, and the control assembly includes a heater and a second temperature sensor disposed above the heater, the second temperature sensor being located directly below the cold mirror 12. The temperature of the heater is collected by a second sensor. The control assembly is arranged in the vicinity of the cold mirror 12, making the temperature control more accurate.
The refrigeration device 8 is provided below the stage 6, and the refrigeration device 8 is connected to the stage 6. The refrigerating device 8 adopts a refrigerator with the model of KDE 415.
In other preferred embodiments, the photodetector 2 is externally connected to an oscilloscope or a voltage acquisition card for observing signal changes. When the dew point is measured, an oscilloscope is used for recording data of the photoelectric detector 2 and drawing a curve, so that errors caused by naked eyes can be reduced, the time of dew condensation and dew elimination and the dew point temperature can be accurately observed, and the time and the dew point temperature are mutually verified with the naked eyes.
Application example 1
The low-temperature gas humidity measurement system based on the embodiment provides an application example of a low-temperature oxygen humidity measurement method, the measurement method is carried out by adopting the low-temperature gas humidity measurement system, and oxygen humidity measurement is converted into dew point temperature measurement by utilizing a cold mirror dew point method. The method specifically comprises the following steps:
installing a low-temperature gas humidity measuring system:
s1: and punching the polished surface of the single-side polished red copper mirror, and connecting the unpolished surface to an objective table 6 of a low-temperature control platform by using low-temperature heat-conducting glue. The zirconium oxynitride temperature sensor is symmetrically arranged on the edge of the polishing surface, and is fixed by using low-temperature heat-conducting glue, so that the bottom surface of the zirconium oxynitride temperature sensor is tightly attached to the polishing surface of the copper mirror. The primary cold shield and the vacuum cover 4 are sequentially installed.
S2: the laser emitter and the photoelectric detector 2 are symmetrically arranged on two sides of the first optical through hole 15 of the vacuum cover 4, the support is adjusted to form a laser light path 14 of the laser emitter, the first optical through hole 15, the second optical through hole 13, the polished copper mirror reflection, the second optical through hole 13, the first optical through hole 15 and the photoelectric detector 2, and a receiving plane of the photoelectric detector 2 is perpendicular to the light path.
S3: two vacuum ports of a vacuum cover 4 of the low-temperature control platform are respectively externally connected with a vacuum gauge and a tee joint 7, a first channel of the tee joint 7 is connected with a first stop valve 16 and then is connected with a vacuum pump 18 through a corrugated pipe, and the first stop valve 16 is opened; the second channel of the three-way valve is connected with a micro-adjusting valve 21, then connected with a second stop valve 22 through an air pipe 25, connected with a pressure reducing valve 23 through the air pipe 25 and finally connected with an oxygen bottle. The oxygen is introduced for 3 to 5 minutes at a flow rate of 1sccm, and then the micro-adjustment valve 21, the second stop valve 22 and the pressure reducing valve 23 are closed in sequence.
Dew point was generated and measured:
s4: and opening the vacuum pump 18 to reduce the pressure inside the cavity of the low-temperature control platform to 5000 Pa. And (3) opening the compressor to enable the low-temperature control platform to cool at full speed, adjusting the cooling speed to 1 ℃/min when the temperature is reduced to-180 ℃, and simultaneously automatically recording the current copper mirror surface temperature value and the current photoelectric detector output signal intensity by the computer at intervals of 1 s. Until the dew condensation linearity appears on the mirror surface, the indication number of the photoelectric detector 2 changes, the copper surface can be observed to be fogged by naked eyes, and the temperature value of the dew point appears is recorded. And then reducing the temperature to 20 ℃ below the dew point temperature, carrying out temperature rise operation, adjusting the temperature rise speed to 1 ℃/min until the dew point disappears, and recording the temperature value at the moment.
S5: and (4) raising the temperature to be 20 ℃ above the temperature value when the dew point recorded in S4 disappears, and repeating the operations of lowering the temperature, raising the temperature and recording the temperature point. The average of the 6 temperature values was taken as the dew point temperature value at that time.
S6: according to the formula (1-1) of the dew point temperature and the oxygen vapor pressure, converting S5 to obtain the oxygen vapor pressure e (T) corresponding to the dew point temperature valued) The concentration is the current oxygen content concentration, then the oxygen saturation vapor pressure e (T) of the working temperature is calculated, and finally the oxygen humidity of the working temperature is calculated through a formula (1-2).
S7: if the oxygen humidity of other concentration needs to be measured, the first stop valve 16 connected with the vacuum pump 18 can be closed, the second stop valve 22 and the pressure reducing valve 23 of the oxygen cylinder are screwed to a very small angle, and oxygen is introduced by the minimum flow of the regulating valve, so that the situation that the vacuum degree is not enough due to the overlarge oxygen concentration is prevented. And repeating the steps S3, S4, S5 and S6 to measure the dew point temperature corresponding to the oxygen concentration.
Application example 2
The low-temperature gas humidity measurement system based on the embodiment provides an application example of a low-temperature nitrogen humidity measurement method, the measurement method is performed by adopting the low-temperature gas humidity measurement system, and nitrogen humidity measurement is converted into dew point temperature measurement by utilizing a cold mirror dew point method. The method specifically comprises the following steps:
installing a low-temperature gas humidity measuring system, and referring to fig. 1:
s1: and punching the polished surface of the single-side polished red copper mirror, and connecting the unpolished surface to an objective table 6 of a low-temperature control platform by using low-temperature heat-conducting glue. The zirconium oxynitride temperature sensor is symmetrically arranged on the edge of the polishing surface, and is fixed by using low-temperature heat-conducting glue, so that the bottom surface of the zirconium oxynitride temperature sensor is tightly attached to the polishing surface of the copper mirror. The primary cold shield and the vacuum cover 4 are sequentially installed.
S2: the laser emitter and the photoelectric detector 2 are symmetrically arranged on two sides of the first optical through hole 15 of the vacuum cover 4, the support is adjusted to form a light path of the laser emitter, the first optical through hole 15, the second optical through hole 13, the polished copper mirror reflection, the second optical through hole 13, the first optical through hole 15 and the photoelectric detector 2, and a receiving plane of the photoelectric detector 2 is perpendicular to the light path.
S3: two vacuum ports of a vacuum cover 4 of the low-temperature control platform are respectively externally connected with a vacuum gauge and a tee joint 7, a first channel of the tee joint 7 is connected with a first stop valve 16 and then is connected with a vacuum pump 18 through a corrugated pipe, and the first stop valve 16 is opened; the second channel of the three-way valve is connected with a micro-regulating valve 21, then connected with a second stop valve 22 through a gas pipe 25, connected with a pressure reducing valve 23 through the gas pipe 25 and finally connected with a nitrogen gas bottle. Firstly, nitrogen is introduced for 3 to 5 minutes at a flow rate of 1sccm, and then the micro-adjustment valve 21, the second stop valve 22 and the pressure reducing valve 23 are closed in sequence.
Dew point was generated and measured:
s4: and opening the vacuum pump 18 to reduce the pressure inside the cavity of the low-temperature control platform to 5000 Pa. And (3) opening the compressor to enable the low-temperature control platform to cool at full speed, adjusting the cooling speed to 1 ℃/min when the temperature is lowered to-190 ℃, and simultaneously automatically recording the current copper mirror surface temperature value and the current photoelectric detector output signal intensity by the computer at intervals of 1 s. Until the dew condensation linearity appears on the mirror surface, the indication number of the photoelectric detector 2 changes, the copper surface can be observed to be fogged by naked eyes, and the temperature value of the dew point appears is recorded. And then reducing the temperature to 20 ℃ below the dew point temperature, carrying out temperature rise operation, adjusting the temperature rise speed to 1 ℃/min until the dew point disappears, and recording the temperature value at the moment.
S5: and (4) raising the temperature to be 20 ℃ above the temperature value when the dew point recorded in S4 disappears, and repeating the operations of lowering the temperature, raising the temperature and recording the temperature point. The average of the 6 temperature values was taken as the dew point temperature value at that time.
S6: according to the formula (1-1) of the dew point temperature and the nitrogen vapor pressure, the nitrogen vapor pressure e (T) corresponding to the dew point temperature value obtained by S5 is convertedd) The concentration is the current oxygen content concentration, then the oxygen saturation vapor pressure e (T) of the working temperature is calculated, and finally the nitrogen humidity of the working temperature is calculated through a formula (1-2).
S7: if the nitrogen humidity of other concentrations needs to be measured, the first stop valve 16 connected with the vacuum pump 18 can be closed, the second stop valve 22 and the pressure reducing valve 23 of the nitrogen cylinder are screwed to a minimum angle, and nitrogen is introduced through the minimum flow of the regulating valve, so that the situation that the vacuum degree is insufficient due to the overlarge nitrogen concentration is avoided. The steps of S3, S4, S5 and S6 are repeated, and the dew point temperature corresponding to the nitrogen concentration is measured. In specific implementation, gases with the normal pressure dew point of less than 25 ℃ such as argon, carbon dioxide, helium and the like can be subjected to low-temperature gas humidity measurement by the measurement method of the application example.
The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention.
Claims (10)
1. A cryogenic gas humidity measurement system comprising:
the dew point generating device is used for generating a dew point and comprises a low-temperature control platform and a cold mirror with a polishing surface, the low-temperature control platform is provided with a closed cavity, and the closed cavity is provided with a refrigerating device used for reducing the temperature of the cold mirror and a temperature control assembly used for controlling the cooling speed; the low-temperature control platform is externally connected with a measuring component for measuring air pressure and a vacuum pump for adjusting the air pressure of the closed chamber; the cold mirror is arranged in the closed cavity as a reflecting mirror surface, and a first temperature sensor is arranged on the cold mirror and used for collecting the surface temperature value of the cold mirror;
a dew point detecting system for judging whether generate dew point, dew point detecting system includes laser emitter and the photoelectric detector who assembles the light filter, laser emitter photoelectric detector symmetry set up in the airtight cavity outside of low temperature accuse temperature platform, by laser emitter cold mirror reaches photoelectric detector forms the light path, wherein laser emitter launches laser warp low temperature accuse temperature platform extremely cold mirror, warp cold mirror reflection extremely photoelectric detector, through photoelectric detector signal obviously changes and judges dew point and generates, according to surveying dew point formation temperature on the cold mirror to obtain the gas humidity that awaits measuring.
2. The cryogenic gas humidity measurement system of claim 1, wherein the cryogenic temperature controlled platform comprises:
the vacuum cover is provided with an accommodating cavity, and a first optical through hole for passing through the light path is formed in the top of the vacuum cover; the vacuum cover is provided with a first vacuum port and a second vacuum port which are respectively externally connected with a vacuum gauge and a tee joint;
the objective table is arranged in the accommodating cavity of the vacuum cover, is a cold transfer and temperature fluctuation inhibition assembly and is used for bearing the cold mirror;
the low-temperature radiation cold screen is arranged in the accommodating cavity of the vacuum cover, the low-temperature radiation cold screen covers the outer portion of the objective table and forms a closed space with the objective table, a second optical through hole used for passing through the light path is formed in the top of the low-temperature radiation cold screen, and the position of the second optical through hole is opposite to that of the first optical through hole from top to bottom.
3. The system for measuring humidity of low-temperature gas as claimed in claim 2, wherein the laser emitter and the photodetector are disposed outside the vacuum enclosure and located at two sides of the first optical through hole respectively, and the light path is formed by the laser emitter, the first optical through hole, the second optical through hole, the cold mirror, the second optical through hole, the first optical through hole and the photodetector in sequence.
4. The system according to claim 2, wherein a first channel of a tee external to the second vacuum port is sequentially connected to the first stop valve and the vacuum pump through a pipeline, and a second channel of the tee is sequentially connected to the micro-regulating valve, the second stop valve, the pressure reducing valve and the gas storage device through a pipeline.
5. A cryogenic gas humidity measurement system according to claim 2,
the temperature control assembly is embedded in the objective table and comprises a heater and a second temperature sensor, the second temperature sensor is arranged above the heater, and the second temperature sensor is positioned right below the cold mirror;
the refrigerating device is arranged below the objective table.
6. A cryogenic gas humidity measurement system according to any one of claims 1 to 5,
adjusting the incident angle of the optical path so that the reflected light is perpendicular to the receiving plane of the photodetector can reduce the interference of the light reflecting surface and other light sources on the photodetector;
the wavelength of the laser emitter is matched with the wavelength range of the optical filter of the photoelectric detector, so that the photosensitive object of the photoelectric sensor is ensured to be incident light of the laser emitter.
7. The system for measuring humidity of low-temperature gas according to any one of claims 1 to 5, wherein the photodetector is externally connected to an oscilloscope or a voltage acquisition card for observing signal changes.
8. A low-temperature gas humidity measurement method is characterized in that the low-temperature gas humidity measurement system of any one of claims 1 to 7 is adopted, and a cold mirror dew point method is utilized to convert the gas humidity measurement to be measured into dew point temperature measurement; the gas to be detected is a gas with a normal pressure dew point of less than 25 ℃, and the gas comprises any one of oxygen, argon, nitrogen, carbon dioxide or helium.
9. The method of measuring humidity of a cryogenic gas of claim 8, comprising:
s1: the polishing surface of the cold mirror faces upwards, and the other surface of the cold mirror is connected to an objective table of a low-temperature control platform by using low-temperature heat-conducting glue;
s2: symmetrically placing low-temperature sensors at the edges of a cold mirror polishing surface, and fixing the bottom surfaces of the low-temperature sensors and the cold mirror polishing surface by adopting low-temperature heat-conducting glue to ensure that the bottom surfaces of the low-temperature sensors are tightly attached to the cold mirror polishing surface;
s3: respectively arranging a first optical through hole and a second optical through hole on the top of the vacuum cover and the top of the low-temperature radiation cold screen, and respectively symmetrically arranging a laser emitter and a photoelectric detector on two sides of the first optical through hole to form a light path of the laser emitter, the first optical through hole, the second optical through hole, the cold mirror reflection, the second optical through hole, the first optical through hole and the photoelectric detector;
s4: connecting a first vacuum port of the low-temperature control platform with a vacuum gauge and connecting a second vacuum port of the low-temperature control platform with a tee joint, wherein a first channel of the tee joint is sequentially connected with a first stop valve and a vacuum pump, and a second channel is sequentially connected with a micro-regulating valve, a second stop valve, a pressure reducing valve and a gas storage device; then, introducing gas to be detected into the vacuum cover through a second channel to fill the cavity and the pipeline, and then closing the micro-regulating valve, the second stop valve and the pressure reducing valve in sequence;
s5: opening a vacuum pump, vacuumizing, closing the vacuum pump, opening a refrigerating device of a low-temperature control platform to cool the low-temperature control platform, starting a temperature control assembly after the low-temperature control platform is cooled to a set temperature, controlling the cooling speed of the low-temperature control platform to enable the low-temperature control platform to cool at a constant speed until a dew point appears, enabling the indication number of a photoelectric detector to change, enabling the polished surface of the cold mirror to be observed to be fogged by naked eyes, and recording the temperature value of a first temperature sensor at the moment as the current dew point temperature; continuing to cool the low-temperature control platform to a set temperature, then carrying out uniform temperature rise operation until the dew point disappears, and recording the temperature value of the first temperature sensor at the moment;
s6: continuing to heat the low-temperature control platform to a set temperature, repeating the operations of cooling and heating and recording the temperature value with the dew point and the temperature value with the dew point disappearing, and taking the average value of a plurality of recorded temperature values as the dew point temperature value at the moment as the time delay condition of human eye error or photoelectric detector capture caused by the dew point disappearing or appearing phenomenon is recorded during the heating and cooling;
s7: and converting the saturated vapor pressure in the cavity of the vacuum cover according to the calculation relationship between the dew point temperature and the saturated vapor pressure of the gas to be detected, namely the content of the gas to be detected in the cavity, and simultaneously obtaining the humidity of the gas to be detected at any temperature.
10. The method of measuring humidity of a cryogenic gas of claim 9, further comprising:
when the relation between the humidity and the dew point temperature of the gas to be detected with different concentrations needs to be researched, under the condition that a first stop valve connected with a vacuum pump is closed in S4, a second stop valve and a pressure reducing valve of a gas storage device are unscrewed for a set angle, the gas to be detected is introduced at the minimum flow of an adjusting valve, and the phenomenon that the vacuum degree is insufficient due to the fact that the concentration of the gas to be detected is too high and the heat insulation effect is lost is prevented; and repeating the steps S5, S6 and S7 to measure the dew point temperature corresponding to the gas concentration, thereby measuring the humidity of the gas to be measured with different concentrations.
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| CN113029967A (en) * | 2021-03-25 | 2021-06-25 | 广东工业大学 | Device and method for measuring air humidity |
| CN113358696A (en) * | 2021-08-10 | 2021-09-07 | 北京亿华通科技股份有限公司 | Dew point temperature detection device and method for fuel cell |
| CN113834586A (en) * | 2021-09-26 | 2021-12-24 | 中国兵器装备集团上海电控研究所 | Flame detector with mirror surface anti-dewing function |
| CN117147091A (en) * | 2023-07-25 | 2023-12-01 | 中国空气动力研究与发展中心设备设计与测试技术研究所 | Maintenance platform for dew point measurement of low-temperature wind tunnel test section and use method |
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